The metal cleaning industry has for years used aqueous acids to remove scale and surface dirt from metals. These aqueous acid solutions are used in such diverse applications as boiler cleaning, radiator cleaning and pickling. The metals cleaned are similarly diverse, aluminum, brass, copper, solder, steel and cast iron. Often two or more of these metals are cleaned in the same system. It is also the habit of the industry to inhibit these acid solutions to prevent attack on the metals being cleaned. Inhibitors known to reduce attack by these acid solutions on brass, copper, solder steel and cast iron are also known to be poor in protecting aluminum. Inhibitors known to be useful to prevent attack on aluminum are generally poor in protecting the other metals and, in addition, are for the most part more toxic and thus less desirable to employ.
Many patents and literature have been published describing combinations or reaction products which are useful to prevent corrosion of ferrous or non-ferrous metals in contact with acid media, although aluminum is usually a special problem. Most of these compositions, as well as the more common industrial compositions, use surface active agents to improve dispersion or compatibility of the active inhibitors in the aqueous acid media and/or the dispersion of the metal salts, resulting from the reaction of the acid with the metal oxides being removed, and the other grime, greases, oils, etc., which the cleaning solution removes. Examples of corrosion inhibitors which incorporate surfactants can be found in Oakes, U.S. Pat. No. 3,017,355, Harrison, et al., U.S. Pat. No. 3,107,221 and Keeney, U.S. Pat. No. 3,802,890 to name but a few. Kaneko, et al., U.S. Pat. No. 3,676,354 discloses a synergistic increase in corrosion inhibition of acid solutions on ferrous metals when a nonionic surfactant is used in combination with an alkanolamine as the principal corrosion inhibitor.
It would be advantageous to provide an inhibitor composition suitable for use in the presence of aqueous acids in conjunction with the several metals including aluminum. It would also be advantageous to provide an inhibitor composition of no more toxicity than those nitrogen containing compounds now in use.